Cystic fibrosis "gene-assist" therapy is a new approach using drugs to restore function to mutant cystic fibrosis transmembrane conductance regulator (CFTR) molecules. The concept that it might be possible to activate mutant CFTR resident in the cystic fibrosis cell has received support from a number of recent experiments. CPX is a new drug in the class of "gene-assist" therapeutics which may interact directly with the CFTR. The primary objective of this study is to evaluate the safety of ascending doses of CPX administered to adult patients with mild CF. The seconday objective is to evaluate the pharmacokinetics. This site exceeded the expected enrollment.